Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $85.78   12.124%   $96.18   $96.18   $96.20   $96.20  
  Purchase #2 $216.97   3.634%   $224.8547   $224.85   $224.85   $224.90  
  Purchase #3 $242.25   11.214%   $269.4159   $269.42   $269.40   $269.40  
  Purchase #4 $28.66   10.658%   $31.7146   $31.71   $31.70   $31.70  
  Purchase #5 $186.83   8.646%   $202.9833   $202.98   $203.00   $203.00  
  Purchase #6 $44.99   4.755%   $47.1293   $47.13   $47.15   $47.10  
  Purchase #7 $119.45   8.357%   $129.4324   $129.43   $129.45   $129.40  
  7 purchase totals = $924.93       $1,001.7102   $1,001.70   $1,001.75   $1,001.70